Record carrier including a servo track having first and second modulated parts representing a data type and a word sync type, respectively, and an apparatus for scanning the record carrier

ABSTRACT

A record carrier has a servo track ( 4 ) indicating an information track ( 9 ) intended for recording information blocks. The servo track ( 4 ) has a periodic variation of a physical parameter at a predetermined frequency and modulated parts for encoding position information at regular intervals. The modulated parts start with a bit sync element and are of a data type having a data bit element, or of a word sync type having a word sync element. The word sync element and the data bit element are modulated according to a same predetermined type of modulation of the periodic variation. The effective strength of a modulated element is the number of periodic variations that are substantially different and available for detection of that element. The effective strength of the word sync element and of the data bit element are equal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. patent application Ser. No.10/268,445, filed Oct. 10, 2002, the contents of which is incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field Of The Invention

The invention relates to a record carrier comprising a servo trackindicating an information track intended for recording informationblocks represented by marks, said servo track having a periodicvariation of a physical parameter at a predetermined frequency andmodulated parts for encoding position information at regular intervals,a first type of modulated parts starting with a bit sync element andbeing of a data type having a data bit element, and a second type ofmodulated parts starting with a bit sync element and being of a wordsync type having a word sync element, the word sync element and the databit element being modulated according to a same predetermined type ofmodulation of the periodic variation.

The invention further relates to a recording and/or playback devicecomprising means for writing and/or reading information blocks in aninformation track on a record carrier having a servo track indicatingthe information track, said device comprising means for scanning theservo track and demodulation means for retrieving position informationfrom a signal generated by a variation of a physical parameter of theservo track at a predetermined frequency, said servo track havingmodulated parts for encoding position information at regular intervals,a first type of modulated parts starting with a bit sync element andbeing of a data type having a data bit element, and a second type ofmodulated parts starting with a bit sync element and being of a wordsync type having a word sync element, the word sync element and the databit element being modulated according to a same predetermined type ofmodulation of the periodic variation.

The invention further relates to a method for manufacturing the recordcarrier.

2. Description Of The Related Art

A record carrier and device for reading and/or writing information areknown from International Patent Application No. WO 00/43996,corresponding to U.S. Pat. Nos. 6,538,982 and 6,765,861 (PHN 17323). Theinformation to be recorded is encoded into an information signal whichincludes address codes and is subdivided in accordance with the addresscodes into information blocks. The record carrier is of a recordabletype and has a servo track, usually called pre-groove, for causing servosignals to be generated when scanning the track. A physical parameter,e.g., the radial position, of the pre-groove periodically varies at apredetermined frequency constituting a so-called wobble. During thescanning of the track, this wobble leads to a variation of the radialtracking servo signals and a wobble signal can be generated. The wobbleis modulated according to a type of modulation using phase modulationfor encoding position information. The phase modulation or frequencymodulation used for encoding digital position information is selected tominimally disturb the component of the predetermined frequency in thewobble signal, because that component is used to control the recordingspeed. Hence, a majority of the periodic variations needs to benon-modulated, i.e., having the zero crossings not shifted from thenominal positions. During recording, the position information isretrieved from the wobble signal and is used for positioning theinformation blocks by keeping a predefined relation between the addresscodes in the information blocks and the position information. Theaddresses are encoded in modulated parts of the wobble starting with abit sync element followed by either a word sync element or a data bitelement.

A problem of the known system is that detection of the word sync elementis not reliable.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a record carrier and devicein which the synchronization is more reliable.

According to the invention, a record carrier as defined in the openingparagraph, is characterized in that the effective strength of the wordsync element and of the data bit element are equal, the effectivestrength being the number of periodic variations that are substantiallydifferent and available for detection of the corresponding element.Further, the recording and/or playback device, as described in theopening paragraph, is characterized in that the demodulation meanscomprises means for detecting the type of the modulated parts across asame effective strength by detecting the word sync element or the databit element, the effective strength being the number of periodicvariations that are substantially different for the correspondingelement. The invention is based on the following recognition. In DVD+RW,the wobble format consists of the following ADIP units (2 indicating amodulated, i.e., inverted, wobble; 0 indicating a not modulated wobble):

-   -   ADIP word sync=“2222000000000000000 . . . ”    -   ADIP ZERO=“2000002200000000000 . . . ”    -   ADIP ONE=“2000220000000000000 . . . ”        The first inverted wobble (indicated by “2”) is the so-called        bit sync. The next three inverted wobbles form the word sync        (“222” in case of a word sync, “000” otherwise). The next four        wobbles carry the ZERO or ONE information (“0022” or “2200”).        After these first 8 wobbles, only positive wobbles follow that        carry no information (but that are important for the PLL        performance). Apart from the bit sync, there are 3 modulated        wobbles for the word sync and only 2 modulated wobbles for the        ONE and the ZERO. The Applicants note that the detection of the        word sync element is less reliable than the detection of a data        bit element, which can be expressed as effective strength.        Further, Applicants recognized that for reliable detection of        all elements with the minimum disturbance of the regular        periodic variations, the same strength for all elements is        desirable. The “L”-number indicates the effective strength of        the modulated element. For the word sync, it has to be decided        whether there is a word sync or not (so compare “222” with        “000”), which has an effective strength of 3 wobbles. For the        bit detection, we have to decide between ONE and ZERO (so        compare “2200” and “0022”), which has an effective strength of        L=4 wobbles. To achieve the same strength for the word sync        detection and the bit detection, one would have to increase the        number of wobbles used for word sync detection by 1, from 3        to 4. Hence, reliable detection in combination with minimal        disturbance of the periodic variations is achieved by selecting        equal effective strength for the data bit and word sync        elements.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be apparent from andelucidated further with reference to the embodiments described, by wayof example, in the following description and with reference to theaccompanying drawings, in which:

FIG. 1 a shows a record carrier with a servo track (top view);

FIG. 1 b shows a servo track (cross section);

FIG. 1 c shows a wobble of a servo track (detail);

FIG. 1 d shows a further wobble of a servo track (detail);

FIG. 2 shows bi-phase wobble modulation;

FIG. 3 shows MSK wobble modulation;

FIG. 4 shows a modulation scheme including split word sync;

FIG. 5 shows a device for reading information blocks; and

FIG. 6 shows a device for writing information blocks.

In the Figures, elements which correspond to elements already describedhave the same reference numerals.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 a shows a disc-shaped record carrier 1 provided with a track 9intended for recording, and a central hole 10. The track 9 is arrangedin accordance with a spiral pattern of windings 3. FIG. 1 b is across-section taken on the line b-b of the record carrier 1, in which atransparent substrate 5 is provided with a recording layer 6 and aprotective layer 7. The recording layer 6 may be optically writable, forexample, via phase change, or magneto-optically writable by a device forwriting information, such as the known CD-Rewritable or CD-Recordable.The recording layer may also be provided with information via aproduction process, in which first a master disc is made, and then thismaster disc is subsequently replicated through pressing. The informationis organized in information blocks and is represented by opticallyreadable marks in the form of a succession of areas reflecting muchradiation and little radiation such as, for example a succession of pitsof different lengths in a CD. In one embodiment, the track 9 on therecord carrier of a rewritable type is indicated by a servo-patternwhich is provided during manufacture of the blank record carrier. Theservo-pattern is formed, for example, by a pre-groove 4 which enables awrite head to follow the track 9 during scanning. The pre-groove 4 maybe implemented as a deeper or a raised part, or as a material propertydeviating from its ambience. Alternatively, the servo-pattern mayconsist of an alternation of elevated and deeper windings, referred toas land and groove patterns, with a transition from land to groove orvice versa taking place per winding. FIGS. 1 c and 1 d show two examplesof a periodical variation of a physical parameter of the pre-groove,called wobble. FIG. 1 c shows variation of the lateral position, andFIG. 1 d shows variation of the width. This wobble produces a wobblesignal in a tracking servo-sensor. The wobble is, for example,frequency-modulated, and position information, such as an address, atime code or winding information, is coded in the modulation. Adescription of a rewritable CD system which is provided with positioninformation in such a way can be found in U.S. Pat. No. 4,901,300 (PHN12.398). A servo-pattern may also consist of, for example, regularlydistributed sub-patterns which periodically cause tracking signals.Further, the servo-pattern may include modifications of the land areabeside the pre-groove, e.g., an undulating pre-groove having landpre-pits in a specific pattern for encoding position information like inDVD-RW.

The variation of the servo track includes relatively large parts ofmonotone wobble, so called non-modulated parts. Further, the servo trackhas relatively short parts where the frequency and/or phase of thewobble deviates from the predetermined wobble frequency, calledmodulated parts. In this document, any servo-pattern of a periodicnature in combination with any additional elements encoding informationis referred to as a servo track having a periodic variation of aphysical parameter at a predetermined frequency, or wobble, that hasmodulated parts.

FIG. 2 shows bi-phase wobble modulation. An upper trace shows the wobblemodulation for a word sync pattern, a second and third trace show thewobble modulations for data bits of the address, the total modulationbeing called Address In Pre-groove (ADIP). Predetermined phase patternsare used for indicating a synchronizing symbol (ADIP bit sync) and asynchronization of the full address word (ADIP word sync), and for therespective data bits (ADIP Data=‘0’, and ADIP data=‘1’). The ADIP bitsync is indicated by a single inverted wobble (wobble # 0). The ADIPword sync is indicated by three inverted wobbles directly following theADIP bit sync, whereas data bits have non-inverted wobbles in this area(wobble # 1 to 3). An ADIP Data area comprises a number of wobbleperiods assigned to represent one data bit, in the Figure, the wobbleperiods numbered 4 up to 7 (=wobble # 4 to 7). The wobble phase in firsthalf of the ADIP Data area is inverse to the wobble phase in the secondhalf of the area. As such, each bit is represented by two sub-areashaving different phases of the wobble, i.e., called bi-phase. Data bitsare modulated as follows: ADIP Data=‘0’ is represented by 2 non-invertedwobbles followed by two inverted wobbles, and ADIP data=‘1’ vice versa.In this embodiment, the modulation for data bits is fully symmetrical,giving equal error probability for both data bit values. However, othercombinations of wobbles and inverted wobbles, or other phase values maybe used. In an embodiment, a predetermined modulation is used after anADIP Word Sync, indicating ‘empty’, instead of a data bit. Monotonewobbles may be used after the first data bit, or further data bits maybe encoded thereafter. Preferably, a large majority of the wobbles isnot modulated (i.e., has the nominal phase) for ensuring an easy lockand a stable output of a PLL in a detector; in this embodiment, the 8possibly modulated wobbles are followed by 85 not modulated (i.e.,monotone) wobbles (wobble # 8 to 92). The output frequency of the PLLhas to be as stable as possible, because during writing, the write clockis derived from the PLL output.

FIG. 3 shows Minimum Shift Keying (MSK) wobble modulation. The MSKmodulation uses a first pattern 31 for transferring a first bit valueand a second pattern 32 for transferring a second bit value. Furthercombinations of the patterns 31, 32 may be used to transfersynchronization information. Each MSK pattern has a central part of atleast one full wobble period, in the first pattern, the central part 34in non-inverted, while in the second pattern, the central part 37 isinverted. Each MSK pattern further has a starting part and an endingpart. The left MSK pattern has a starting part 33 and an ending part 35just being a single wobble period. The right MSK pattern has a startingpart 36, which inverts the phase by having a frequency of 1.5 times thewobble frequency, i.e., by having 3 half sine periods within one wobblefrequency period. The ending part is similar to re-invert the phase tothe non-inverted state. Detection of MSK data bits is primarily based onthe detection of the central part, because both central parts exhibitthe maximum difference between the two patterns. In addition, thedifference of the not modulated starting part 33 and modulated startingpart 36, and the not modulated ending part 35 and modulated ending part38 can be exploited for detection, the total length of these differencesbeing estimated to have 50% of effective strength of detection whencompared to the central part. The MSK encoding can be used to encodeaddress bits in a pre-groove wobble, but the pre-groove wobble needs tobe not modulated for the majority of wobble periods. The large majorityof not modulated wobbles is needed for reliably controlling the rotationspeed of the disc and/or the write clock of the recording process.

FIG. 4 shows a modulation scheme with split word sync based on the MSKwobble modulation. In each cell of the matrix shown, a zero indicates anot modulated wobble, a one indicates a starting part of 1,5 wobble toinvert the phase, a two indicates an inverted wobble, and a threeindicates an ending part of 1,5 wobble to re-invert the phase to thenormal state, as described above with reference to FIG. 3. In each rowof the matrix, 56 consecutive wobbles are indicated (columns 37-54 allbeing zero), and each row starts with a bit sync element in columns0,1,2. A total ADIP address word comprises 83 rows, and the rows arenumbered according to their ADIP bit number. The ADIP bits numbered0,2,4,6 and 8,13,18, etc are isolated bit syncs (40,41). The ADIP wordincludes several word sync elements, which all comprise two partialelements separated by a number of not modulated wobbles. Such syncelements are referred to as split word sync. In ADIP bit 1 there is afirst split word sync element called sync0, and in ADIP bits 3,5,7,there are three further split word sync elements sync1, sync2 and sync3.All split word sync elements have a different location for maximumreliability of detection. Starting at ADIP bit 8, there is a repetitivepattern of 5 rows consisting of one isolated bit sync followed by 4 databits; the values of the data bit elements in the Figure being arbitraryexamples. Hence, in total, 13×4=52 data bits are available in the ADIPaddress word. The effective strength of the MSK modulated elements isindicated by the “L”-number: 2 wobbles for “L=2” marks, even though themodulation extends for 3 wobble periods. As explained above for MSK, thestarting and ending parts are considered to have an effective strengthof 50%, hence, the total of a central part of 1 wobble and 2starting/ending wobbles at 50% accumulates to L=2. In an embodiment, themethod of detection requires even values, e.g., “L=2” and “L=4”, becausein that case, the total number of wobbles in an ADIP unit (56) can bedivided by the L-value. In constructing the scheme, the followingproblem is solved:

1. For detection, it is an advantage to have only 1 type of modulatedelement: so only “L=2” elements or only “L=4” elements. In that case,one only has to build one detector or filter to detect the elements, andnot 2 different detectors or filters.

2. To have similar strength of the word sync detection and bitdetection, one would need “L=2” elements for bits (ONE or ZERO) and“L=4” elements for word syncs.

The problem is how to balance these 2 requirements. One unsuitableoption is to use a single “L=2” element for both the bits and the wordsyncs. But this means that the word sync is weaker than required, andthis will then be the weakest link in the detection scheme. Anotherunsuitable option is to use a single “L=4” element for both the bits andthe word syncs. But this means that the bit detection is unnecessarilystrong. This is, of course, no problem for bit detection, but one shouldkeep in mind that these modulated elements disturb the PLL, and usingelements that are too long implies unnecessary distortion of the PLL.The solution is to use a single “L=2” element for the bits ONE and ZERO,and 2 “L=2” elements for the word syncs. In this way, the appropriatestrengths are given to both bits and word syncs while retaining theadvantage of using only a single element, so that only one type ofelement detecting is required. By using a fixed distance between the 2“L=2” elements of a word sync, the detection of the word sync is thesame as adding the outcome of the detector of a single “L=2” element at2 points in time, at the distance between these points is fixed.

In an embodiment, the distance between the “L=2” elements of a word syncis fixed at 8 wobble periods, and for the word syncs the followingsequences are proposed:

-   -   ‘12300000123000001230000000000000000000000000000000000000’        (sync0)    -   ‘12300000001230000012300000000000000000000000000000000000’        (sync1)    -   ‘12300000000012300000123000000000000000000000000000000000’        (sync2)    -   ‘12300000000000123000001230000000000000000000000000000000’        (sync3),        and for the bits the following sequences:    -   ‘1230xxxxx00000000000000000000000000000000000000000000000’ (0 or        1).

The sequence ‘xxxxx’ is either ZERO or ONE as follows:

-   -   ONE: ‘12300’    -   ZERO: ‘00123’

FIGS. 5 shows a reading device for scanning a record carrier 1. Writingand reading of information on optical discs and formatting, errorcorrecting and channel coding rules, are well-known in the art, e.g.,from the CD system. The apparatus of FIG. 5 is arranged for reading therecord carrier 1, this record carrier being identical to the recordcarriers shown in FIG. 1. The device is provided with a read head 52 forscanning the track on the record carrier, and read control meanscomprising drive unit 55 for rotating the record carrier 1, a readcircuit 53, for example, comprising a channel decoder and an errorcorrector, tracking unit 51 and a system control unit 56. The read headcomprises optical elements of the usual type for generating a radiationspot 66 focused on a track of the recording layer of the record carriervia a radiation beam 65 guided through optical elements. The radiationbeam 65 is generated by a radiation source, e.g., a laser diode. Theread head further comprises a focusing actuator for focusing theradiation beam 65 on the recording layer and a tracking actuator 59 forfine positioning of the spot 66 in radial direction on the center of thetrack. The apparatus has a positioning unit 54 for coarsely positioningthe read head 52 in the radial direction on the track. The trackingactuator 59 may comprise coils for radially moving an optical element,or may be arranged for changing the angle of a reflecting element on amovable part of the read head or on a part on a fixed position in thecase part of the optical system is mounted in a fixed position. Theradiation reflected by the recording layer is detected by a detector ofa usual type, e.g., a four-quadrant diode, for generating a detectorsignals 57 including a read signal, a tracking error and a focusingerror signal. The tracking unit 51 is coupled to the read head forreceiving the tracking error signal from the read head and controllingthe tracking actuator 59. During reading, the read signal is convertedinto output information, indicated by arrow 64, in the read circuit 53.The apparatus is provided with a demodulator 50 for detecting andretrieving the address information from the wobble signal included inthe detector signals 57 when scanning the servo track of the recordcarrier. The device is further provided with a system control unit 56for receiving commands from a controlling computer system or from a userand for controlling the apparatus via control lines 58, e.g., a systembus connected to the drive unit 55, the positioning unit 54, thedemodulator 50, the tracking unit 51 and the read circuit 53. To thisend, the system control unit comprises control circuitry, for example, amicroprocessor, a program memory and control gates, for performing theprocedures described below. The system control unit 56 may also beimplemented as a state machine in logic circuits. The read device isarranged for reading a disc having tracks having a periodic variation,e.g., a continuous wobble. The read control unit is arranged fordetecting the periodic variations and for reading, in dependencethereon, a predetermined amount data from the track. In particular, thedemodulator 50 is arranged for reading position information from themodulated signal derived from the modulated wobble. The demodulator 50has a detection unit for detecting modulated wobbles starting at the bitsync elements in the wobble signal which arrive after a long sequence ofnon modulated wobbles. The demodulator further has a word detection unitfor retrieving the words of address information based on the word syncelements. The beginning of such a word is detected from a wordsynchronization signal after the bit sync element. The value of a databit is detected based on the data bit elements encoded by modulatedwobbles. Further, the device has a synchronization unit 67 for detectingthe word sync elements. In the modulation scheme described above withreference to FIG. 4, word syncs are included that have two modulatedpartial elements separated by an interval of not modulated periodicvariations. The synchronization unit 67 detects the partial elements atthe predefined distance, and, from the result, detects the word syncelement. In a preferred embodiment, the demodulator 50 andsynchronization unit 67 share a filter unit for detecting one singletype of modulated element, in particular, in the case that the modulatedparts of the data bits have the same structure as the two modulatedpartial elements of the word sync element.

FIG. 6 shows a device for writing information on a record carrier,according to the invention, of a type which is (re)writable in, forexample, a magneto-optical or optical manner (via phase change or dye)by means of a beam 65 of electromagnetic radiation. The device is alsoequipped for reading and comprises the same elements as the apparatusfor reading described above with FIG. 5, except that it has a write/readhead 62 and recording control means which comprises the same elements asthe read control means, except for a write circuit 60 that comprises,for example, a formatter, an error encoder and a channel encoder. Thewrite/read head 62 has the same function as the read head 52 togetherwith a write function and is coupled to the write circuit 60. Theinformation presented to the input of the write circuit 60 (indicated bythe arrow 63) is distributed over logical and physical sectors accordingto formatting and encoding rules, and converted into a write signal 61for the write/read head 62. The system control unit 56 is arranged forcontrolling the write circuit 60 and for performing the positioninformation recovery and positioning procedure as described above forthe reading apparatus. During the writing operation, marks representingthe information are formed on the record carrier. The recording controlmeans is arranged for detecting the periodic variations, for example, bylocking a phase-locked loop to the periodicity thereof. The demodulator50 and the synchronization unit 67 are described above with reference toFIG. 5.

Although the invention has been explained by embodiments using a wobblemodulation, any other suitable parameter of the track may be modulated,e.g., the track width. Also, for the record carrier, an optical disc hasbeen described, but other media, such as a magnetic disc or tape, may beused. It is noted, that in this document the word ‘comprising’ does notexclude the presence of other elements or steps than those listed, andthe word ‘a’ or ‘an’ preceding an element does not exclude the presenceof a plurality of such elements, that any reference signs do not limitthe scope of the claims, that the invention may be implemented by meansof both hardware and software, and that several ‘means’ may berepresented by the same item of hardware. Further, the scope of theinvention is not limited to the embodiments, and the invention lies ineach and every novel feature or combination of features described above.

1. A record carrier comprising a servo track indicating an information track for recording information blocks represented by marks, said servo track having a periodic variation of a physical parameter at a predetermined frequency, and modulated parts for encoding position information at regular intervals, said modulated parts including a first type starting with a bit sync element and representing a data type having a data bit element, and a second type starting with a bit sync element and representing a word sync type having a word sync element, the word sync element and the data bit element being modulated according to a same predetermined type of modulation of the periodic variation, and the word sync element and the data bit element having equal effective strengths, the effective strength being the number of periodic variations that are substantially different and available for detection of the corresponding element.
 2. The record carrier as claimed in claim 1, wherein the word sync element comprises two modulated partial elements separated by an interval of not modulated periodic variations.
 3. The record carrier as claimed in claim 2, wherein both partial elements are equal.
 4. The record carrier as claimed in claim 1, wherein the data bit element comprises portions of equal length, one portion being a modulated partial element and one portion being not modulated according to a bi-phase modulation.
 5. The record carrier as claimed in claim 1, wherein the predetermined type of modulation is minimum shift keying modulation of the periodic variation.
 6. A recording and/or playback device comprising: means for writing and/or reading information blocks in an information track on a record carrier having a servo track indicating the information track; means for causing said writing and/or reading means to scan the servo track; and demodulation means, coupled to said writing and/or reading means, for retrieving position information from a signal generated by a variation of a physical parameter of the servo track at a predetermined frequency, said servo track having modulated parts for encoding position information at regular intervals, said modulated parts including a first type starting with a bit sync element and representing a data type having a data bit element, and a second type starting with a bit sync element and representing a word sync type having a word sync element, the word sync element and the data bit element being modulated according to a same predetermined type of modulation of the periodic variation, the demodulation means comprising means for detecting the type of the modulated parts across a same effective strength by detecting the word sync element or the data bit element, the effective strength being the number of periodic variations that are substantially different for the corresponding element.
 7. The recording and/or playback device as claimed in claim 6, wherein the means for detecting the type of the modulated parts detects the word sync element from two partial elements that are separated by an interval of not modulated periodic variations.
 8. The recording and/or playback device as claimed in claim 6, wherein the means for detecting the type of the modulated parts detects a modulated partial element, the word sync element comprising two of the modulated partial elements separated by an interval of not modulated periodic variations, and/or the data bit element comprising portions of equal length, one portion being the modulated partial element and one portion being not modulated according to a bi-phase modulation.
 9. A method of manufacturing a record carrier, in which the record carrier is provided with a servo track indicating an information track intended for recording information blocks, which servo track is provided with a variation of a physical parameter at a predetermined frequency and modulated parts for encoding position information at regular intervals, a first type of modulated parts starting with a bit sync element and being of a data type having a data bit element, and a second type of modulated parts starting with a bit sync element and being of a word sync type having a word sync element, the word sync element and the data bit element being modulated according to a same predetermined type of modulation of the periodic variation, the word sync element and the data bit element having equal effective strengths, the effective strength being the number of periodic variations that are substantially different and available for detection of the corresponding element.
 10. The record carrier as claimed in claim 2, wherein the data bit element comprises portions of equal length, one portion being a modulated partial element and one portion being not modulated according to a bi-phase modulation.
 11. The record carrier as claimed in claim 2, wherein the predetermined type of modulation is minimum shift keying modulation of the periodic variation.
 12. The record carrier as claimed in claim 3, wherein the data bit element comprises portions of equal length, one portion being a modulated partial element and one portion being not modulated according to a bi-phase modulation.
 13. The record carrier as claimed in claim 3, wherein the predetermined type of modulation is minimum shift keying modulation of the periodic variation.
 14. The recording and/or playback device as claimed in claim 6, wherein the means for detecting the type of the modulated parts detects a modulated partial element, the word sync element comprising two of the modulated partial elements separated by an interval of not modulated periodic variations, and/or the data bit element comprising portions of equal length, one portion being the modulated partial element and one portion being not modulated according to a bi-phase modulation. 